Research and development on region extraction technologies have been extensively conducted. With such technology, a moving object is detected by extracting an image region of the moving object (referred to as the moving object region hereafter) from an image including an image of the moving object (the image of the moving object is simply referred to as the “moving object” hereafter). Especially when the moving object is a pedestrian, extraction of an image region of the pedestrian is a basic technology commonly used for: focus control and image quality improvement by a digital video camera or a digital still camera; a safe driving support system for automobiles; and human-robot collision avoidance control performed by a robot or collision warning given by the robot.
Common examples of the technology for extracting the moving object region from the image include the following two methods. One is a method of determining the moving object region by evaluating similarity between a previously-prepared moving object model and a moving-object-region candidate in the image. The other is a method of determining the moving object region by segmenting the image into subregions, calculating the amount of characteristics for each of the subregions, and then integrating the subregions similar based on the amounts of characteristics.
Representative examples of the former method include the following method. Firstly, moving-object-region candidates are extracted from the image. After this, similarity between a previously-prepared moving object model and each of the candidates is evaluated, and the region with high similarity is extracted as the moving image region. Moreover, for the case where the region of the moving object, such as a pedestrian, that moves with deformation is extracted, there is a method whereby a moving object model that considers the change in shape is used. For example, Patent Literature 1 discloses a method of extracting a silhouette image of a moving object from images as moving-object-region candidates. With this method, similarity between a parameterized model corresponding to the change in shape of the moving object and the extracted silhouette image is evaluated so as to estimate a region with high similarity and a parameter of the model. Thus, the parameterized model can be applied to the image of the moving object such as a pedestrian that moves with deformation in a cyclic manner, and therefore the moving object region can be extracted.
Representative examples of the latter method include the following method. An image is temporarily segmented into subregions, and the amount of characteristics is calculated based on a pixel luminance value for each of the subregions. Then, similarity in the amount of characteristics is evaluated between the subregions, and the highly-similar subregions are integrated into one moving object region. For example, Patent Literature 2 discloses a method whereby: an image is temporarily segmented into rectangular subregions; the amount of characteristics is calculated based on luminance and motion information for each of the subregions; and then the moving object region can be extracted by integrating the subregions based on order of similarity in the amount of characteristics.